Fuel Endurance + Reserve Calculator estimates available endurance and range after applying explicit reserve policy. It is useful for coastal and offshore passage planning where usable trip fuel must exclude safety reserve. The tool returns reserve volume, trip fuel, endurance hours, and range at planned speed. Use it to compare conservative vs aggressive reserve policies before departure.
Use this calculator as one part of a broader passage-planning workflow. The
Marine Navigation Calculators toolkit
explains how CPA/TCPA, UKC, tide windows, route distance, set and drift, fuel range, and manoeuvring checks fit together.
You can also browse the full
Marine & Navigation category.
Enter the vessel, route, tide, current, or clearance assumptions exactly as labelled, then verify the result against official data and onboard judgment.
How to use this tool
Enter usable fuel onboard, burn rate, reserve percentage, and cruise speed.
Run the calculation to compute reserve fuel and trip-usable fuel.
Review endurance and range outputs and verify they match route plus contingency.
Fuel Inputs
Result
Reserve fuel: 135.00 L
Trip fuel available: 765.00 L
Endurance: 11.77 h
Range: 164.77 nm
Formula or method
Combines the entered navigation assumptions with the tool's planning formula or rule set; it does not replace official navigation sources.
Worked example
Checking fuel range with reserve
Usable fuel: 400 L
Burn rate: 40 L/h
Reserve: 25%
Cruise speed: 8 kn
Result: The calculator separates reserve fuel from trip-usable fuel, then estimates endurance hours and range.
Compare the range with planned route distance plus weather, traffic, diversion, and holding contingencies.
How to interpret the result
Reserve fuel is intentionally excluded from planned trip fuel.
Endurance assumes the entered burn rate remains constant.
Range changes quickly with speed, sea state, current, load, hull condition, and generator or hotel loads.
Conservative reserve policy is important when diversion options are limited.
Common mistakes
Planning range from total fuel instead of trip-usable fuel after reserve.
Using a calm-water burn rate for rough-weather or adverse-current passages.
Forgetting generator, heating, auxiliary, or maneuvering fuel use.
Treating calculated range as a promise instead of a planning estimate.
Burn rate treated as constant at planned operating condition.
Does not account for generator loads, weather detours, or holding patterns.
Review note and limitations
Method - constant burn-rate endurance and range estimate with explicit reserve subtraction.
Does not replace official charts, notices, tide/current data, instruments, pilotage guidance, COLREGs obligations, or navigational judgment.
Planning support only. Confirm fuel plans with vessel data, measured consumption, weather, route risks, local requirements, and prudent seamanship.
FAQ
Should reserve fuel be included in planned range?
No. Reserve fuel is a safety margin and should not be treated as routine trip fuel.
Why can real range differ from calculated range?
Burn rate changes with speed, sea state, current, hull condition, load, engine state, and auxiliary fuel use.
What reserve percentage should I use?
It depends on vessel, route, weather, diversion options, regulation, and operator policy. Use conservative assumptions when uncertainty is high.
Related tools and workflows
Related marine tools help connect the calculation with route planning, clearance, drift, tide, encounter, or fuel checks. Start with CPA/TCPA Risk Calculator, Under Keel Clearance Calculator, and Tide Window Planner when you need a quick follow-up check.